Total microcystin determination using erythro-2-methyl-3-(methoxy-d3)-4-phenylbutyric acid (MMPB-d3) as the internal standard

Metabolomics Applied to Cyanobacterial Toxins and Natural Products

The biological and chemical diversity of Cyanobacteria is remarkable. These ancient prokaryotes are widespread in nature and can be found in virtually every habitat on Earth where there is light and water. They are producers of an array of secondary metabolites with important ecological roles, toxic effects, and biotechnological applications. The investigation of cyanobacterial metabolites has benefited from advances in analytical tools and bioinformatics that are employed in metabolomic analyses. In this chapter, we review selected articles highlighting the use of targeted and untargeted metabolomics in the analyses of secondary metabolites produced by cyanobacteria. Here, cyanobacterial secondary metabolites have been didactically divided into toxins and natural products according to their relevance to toxicological studies and drug discovery, respectively. This review illustrates how metabolomics has improved the chemical analysis of cyanobacteria in terms of speed, sensitivity, selectivity, and/or coverage, allowing for broader and more complex scientific questions.

Analysis of Total-Forms of Cyanotoxins Microcystins in Biological Matrices: A Methodological Review

Microcystins (MCs) are cyclic heptapeptidic toxins produced by many cyanobacteria. Microcystins can be accumulated in various matrices in two forms: a free cellular fraction and a covalently protein-bound form. To detect and quantify the concentration of microcystins, a panel of techniques on various matrices (water, sediments, and animal tissues) is available. The analysis of MCs can concern the free or the total (free plus covalently bound) fractions. Free-form analyses of MCs are the most common and easiest to detect, whereas total-form analyses are much less frequent and more complex to achieve. The objective of this review is to summarize the different methods of extraction and analysis that have been developed for total forms. Four extraction methods were identified: MMPB (2-methyl-3-methoxy-4-phenylbutyric acid) method, deconjugation at basic pH, ozonolysis, and laser irradiation desorption. The study of the bibliography on the methods of extraction and analysis of the total forms of MCs showed that the reference method for the subject remains the MMPB method even if alternative methods and, in particular, deconjugation at basic pH, showed results encouraging the continuation of the methodological development on different matrices and on naturally-contaminated samples.

A Mini-Review on Detection Methods of Microcystins

Cyanobacterial harmful algal blooms (CyanoHABs) produce microcystins (MCs) which are associated with animal and human hepatotoxicity. Over 270 variants of MC exist. MCs have been continually studied due of their toxic consequences. Monitoring water quality to assess the presence of MCs is of utmost importance although it is often difficult because CyanoHABs may generate multiple MC variants, and their low concentration in water. To effectively manage and control these toxins and prevent their health risks, sensitive, fast, and reliable methods capable of detecting MCs are required. This paper aims to review the three main analytical methods used to detect MCs ranging from biological (mouse bioassay), biochemical (protein phosphatase inhibition assay and enzyme linked immunosorbent assay), and chemical (high performance liquid chromatography, liquid chromatography-mass spectrometry, high performance capillary electrophoresis, and gas chromatography), as well as the newly emerging biosensor methods. In addition, the current state of these methods regarding their novel development and usage, as well as merits and limitations are presented. Finally, this paper also provides recommendations and future research directions towards method application and improvement.

Effect of chlorination by-products on the quantitation of microcystins in finished drinking water

Microcystins are toxic peptides that can be produced by cyanobacteria in harmful algal blooms (HABs). Various analytical techniques have been developed to quantify microcystins in drinking water, including liquid chromatography tandem mass spectrometry (LC/MS/MS), enzyme linked immunosorbent assay (ELISA), and oxidative cleavage to produce 2-methyl-3-methoxy-4-phenylbutyric acid (MMPB) with detection by LC/MS/MS, the "MMPB method". Both the ELISA and MMPB methods quantify microcystins by detecting a portion of the molecule common to most microcystins. However, there is little research evaluating the effect of microcystin chlorination by-products potentially produced during drinking water treatment on analytical results. To evaluate this potential, chlorinated drinking water samples were fortified with various microcystin congeners in bench-scale studies. The samples were allowed to react, followed by a comparison of microcystin concentrations measured using the three methods. The congener-specific LC/MS/MS method selectively quantified microcystins and was not affected by the presence of chlorination by-products. The ELISA results were similar to those obtained by LC/MS/MS for most microcystin congeners, but results deviated for a particular microcystin containing a variable amino acid susceptible to oxidation. The concentrations measured by the MMPB method were at least five-fold higher than the concentrations of microcystin measured by the other methods and demonstrate that detection of MMPB does not necessarily correlate to intact microcystin toxins in finished drinking water.

Transformation of microcystins to 2-methyl-3-methoxy-4-phenylbutyric acid by room temperature ozone oxidation for rapid quantification of total microcystins

Microcystins (MCs) are cyanobacterial hepatotoxins capable of accumulation into animal tissues. To determine the total microcystins in water, a novel analytical method, including ozonolysis, methylation of 2-methyl-3-methoxy-4-phenylbutyric acid (MMPB) with methylchloroformate (MCF) and gas chromatography mass spectrometry (GC-MS) detection was developed. The results show that MCs can be oxidized by ozone to produce MMPB at ambient temperature, proving ozonation is an effective, rapid and green method for the transformation of MCs to MMPB without secondary pollution. The oxidation conditions as well as the esterification process were optimized and, subsequently applied to analysis of environmental samples. The method shows wide linear range and high sensitivity with a detection limit of 0.34 μg L(-1). The established method was successfully applied to the analysis of microcystins in water samples.

Oxidative effects and toxin bioaccumulation after dietary microcystin intoxication in the hepatopancreas of the crab Neohelice (Chasmagnathus) granulata

We studied the accumulation and depuration of microcystin-LR (MCLR) in the hepatopancreas of the crab Neohelice granulata fed twice weekly with either non toxic or MCLR-producing Microcystis aeruginosa (strain NPDC1 or NPJB, respectively) during seven weeks. We also analyzed MCLR effects on the oxidative stress- and detoxification-related variables, superoxide dismutase and glutathione-S-transferase activities, and the levels of reduced glutathione and lipid peroxidation (as thiobarbituric acid reactive substances, TBARS). Hepatopancreas MCLR content slightly increased during the first three weeks, up to 8.81±1.84ngg(-1) wet tissue mass (WTM) and then started to decrease to a minimum of 1.57±0.74ngg(-1) WTM at the seventh week (p<0.05 with respect to that in the first week). TBARS levels were about 55% higher in treated than in control N. granulata (p<0.001 and p<0.05) during the first three weeks of the experimental period. GSH content became 50% lower than in control individuals (p<0.01) during weeks 6 and 7. SOD activity was increased by about 2-fold (p<0.05 or p<0.001) from week 3 to 7 in treated crabs with respect to control ones, while GST activity was about 70% higher in treated than in control crabs from week 4 to week 7 (p<0.05). Our data suggest that in the hepatopancreas of N. granulata MCLR accumulation and oxidative damage are limited and reversed by detoxification-excretion and antioxidant mechanisms. The activation of these defensive mechanisms becomes evident at 3-4 weeks after the start of the intoxication.

State of knowledge and concerns on cyanobacterial blooms and cyanotoxins

Cyanobacteria are ubiquitous microorganisms considered as important contributors to the formation of Earth's atmosphere and nitrogen fixation. However, they are also frequently associated with toxic blooms. Indeed, the wide range of hepatotoxins, neurotoxins and dermatotoxins synthesized by these bacteria is a growing environmental and public health concern. This paper provides a state of the art on the occurrence and management of harmful cyanobacterial blooms in surface and drinking water, including economic impacts and research needs. Cyanobacterial blooms usually occur according to a combination of environmental factors e.g., nutrient concentration, water temperature, light intensity, salinity, water movement, stagnation and residence time, as well as several other variables. These environmental variables, in turn, have promoted the evolution and biosynthesis of strain-specific, gene-controlled metabolites (cyanotoxins) that are often harmful to aquatic and terrestrial life, including humans. Cyanotoxins are primarily produced intracellularly during the exponential growth phase. Release of toxins into water can occur during cell death or senescence but can also be due to evolutionary-derived or environmentally-mediated circumstances such as allelopathy or relatively sudden nutrient limitation. Consequently, when cyanobacterial blooms occur in drinking water resources, treatment has to remove both cyanobacteria (avoiding cell lysis and subsequent toxin release) and aqueous cyanotoxins previously released. Cells are usually removed with limited lysis by physical processes such as clarification or membrane filtration. However, aqueous toxins are usually removed by both physical retention, through adsorption on activated carbon or reverse osmosis, and chemical oxidation, through ozonation or chlorination. While the efficient oxidation of the more common cyanotoxins (microcystin, cylindrospermopsin, anatoxin and saxitoxin) has been extensively reported, the chemical and toxicological characterization of their by-products requires further investigation. In addition, future research should also investigate the removal of poorly considered cyanotoxins (β-methylamino-alanine, lyngbyatoxin or aplysiatoxin) as well as the economic impact of blooms.

Monitoring approaches for a toxic cyanobacterial bloom

Cyanobacterial blooms, dominated by Microcystis sp. and associated microcystin variants, have been implicated in illnesses of humans and animals. Little is known regarding the formation of blooms and the presence of cyanotoxin variants in water bodies. Furthermore, the role played by ecological parameters, in regulating Microcystis blooms is complicate and diverse. Local authorities responsible for water management are often faced with the challenging task of dealing with cyanobacterial blooms. Therefore, the development of suitable monitoring approaches to characterize cyanobacterial blooms is an important goal. Currently, various biological, biochemical and physicochemical methods/approaches are being used to monitor cyanobacterial blooms and detect microcystins in freshwater bodies. Because these methods can vary as to the information they provide, no single approach seemed to be sufficient to accurately monitor blooms. For example, immunosensors are more suited for monitoring the presence of toxins in clear water bodies while molecular methods are more suited to detect potentially toxic strains. Thus, monitoring approaches should be tailored for specific water bodies using methods based on economic feasibility, speed, sensitivity and field applicability. This review critically evaluates monitoring approaches that are applicable to cyanobacterial blooms, especially those that focus on the presence of Microcystis, in freshwater bodies. Further, they were characterized and ranked according to their cost, speed, sensitivity and selectivity. Suggested improvements were offered as well as future research endeavors to accommodate anticipated environmental changes.

Soil-based treatments of mechanically collected cyanobacterial blooms from Lake Taihu: efficiencies and potential risks

In China, mechanical collection of cyanoblooms followed by soil-based treatments has been widely used as emergency strategies in many eutrophicated freshwaters. This study was to evaluate both efficiencies and potential risks of typical soil-based technologies. Results from this study indicated that over 90% of cyanobacterial biomass and 96% of dissolved microcystins (MCs) could be restrained in soils via three-level systems, which were much better than single-level systems. High concentrations of MCs, ranged from 65 to 276 ng g⁻¹ and from 2.12 to 6.6 ng g⁻¹, were found in soils around treatment systems and croplands, respectively. In the soil solutions, MCs ranged from 0.35 to 2.0 μg L⁻¹, showing a potentially high leaching risk. In the samples from shallow groundwater near the treatment systems, MC concentrations were detected as high as 1.2 μg L⁻¹. Moreover, bioaccumulations of MCs varied between 22 and 365 μg kg⁻¹, and 19-222 μg kg⁻¹ were found in 13 kinds of crops and 7 kinds of wild grass, respectively. Our results indicated for the first time that current soil-based technologies were effective but could pose potential environmental, ecological, and public health risks. Further improvements of these technologies were also proposed based on our findings.

Determination of microcystin-LR in water by a label-free aptamer based electrochemical impedance biosensor

In this study, an electrochemical impedance biosensor for cyanobacterial toxin microcystin-LR (MC-LR) detection has been developed. MC-LR aptamers were immobilized on the gold electrode through Au-S interaction, in the presence of target (MC-LR); the binding of MC-LR and aptamers probe led to a complex formation change on the electrode surface and resulted in the impedance decreasing. The decrease rate had a linear relationship with logarithm of the MC-LR concentration in the range of 1.0 × 10(-7)-5.0 × 10(-11)mol/L, with a detection limit of 1.8 × 10(-11)mol/L. The sensor has good selectivity and stability, it has been applied to detect MC-LR in three kinds of real water samples with satisfying results.

Detection of total microcystin in fish tissues based on lemieux oxidation, and recovery of 2-methyl-3-methoxy-4-phenylbutanoic acid (MMPB) by solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC/MS)

Microcystins (MCs) are widespread cyanobacterial toxins in freshwater systems, and have been linked to both acute and chronic health effects. A growing number of studies suggest that MC can bioaccumulate in food webs. Although, several methods (i.e. ELISA, LC-MS) have been developed for analysis of MC in water, extraction (for subsequent analysis) of the toxin from biological matrices (i.e. animal tissues) is impeded owing to covalent binding of toxins and active sites of their cellular targets, i.e. protein phosphatases. As an alternative approach, chromatographic methods for analysis of a unique marker, 2-methyl-3-methoxy-4-phenylbutanoic acid (MMPB), the product of the Lemieux oxidation of MCs, have been previously developed, and shown to measure total (bound and unbound) MC. Application, however, has been limited by poor recovery of the analyte. An improved recovery method is proposed - specifically the use of solidphase microextraction (SPME). The MMPB analogue, 4-phenylbutanoic acid (4PB), and oxidized MC, were used to develop methods, and we specifically investigated several SPME fibres, and post-oxidation steps. Specifically, a method employing post-oxidation methyl esterification, followed by headspace SPME recovery of MMPB, was developed, and subsequently applied to analysis of environmental samples (i.e. fish tissues) previously shown to contain MCs. The method shows high linearity for both water and tissues spiked with MC, and an improved limit of quantitation of approximately 140 ng g(-1). Evaluation of field samples by SPME-GC/MS detected considerably higher levels of MC, than detected by conventional methods (i.e. ELISA), and it is proposed that this technique reveals MC (particularly in the bound form) that is not detected by these methods. These results indicate that the developed method provides improved detection capability for MC in biological matrices, and will enhance our ability to understand bioaccumulation in freshwater food webs, as well as monitor exposure.

Detection of free and covalently bound microcystins in animal tissues by liquid chromatography-tandem mass spectrometry

Microcystins are cyanobacterial hepatotoxins capable of accumulation into animal tissues. The toxins act by inhibiting specific protein phosphatases and both non-covalent and covalent interactions occur. The 2-methyl-3-methoxy-4-phenylbutyric acid (MMPB) method determines the total, i.e. the sum of free and protein-bound microcystin in tissues. The aim of the method development in this paper was to tackle the problems with the MMPB methodology: the rather laborious workflow and the loss of material during different steps of the method. In the optimised workflow the oxidation recovery was of acceptable level (29-40%), the extraction efficiency good (62-97%), but the signal suppression effect from the matrix remained severe in our system (16-37% signal left). The extraction efficiency for the determination of the free, extractable microcystins, was found to be good, 52-100%, depending on the sample and the toxin variant and concentration.

First reported case of turtle deaths during a toxic Microcystis spp. bloom in Lake Oubeira, Algeria

Microcystins analysis was conducted in field cyanobacterial bloom samples and dead terrapin tissues from Lake Oubeira (Algeria) with an aim of studying the cause of the mortality of the freshwater terrapin species Emys orbicularis and Mauremys leprosa during October 2005. The deaths of these two terrapin species were observed during a bloom of Microcystis spp. The total microcystin content per phytoplankton biomass evaluated with the methanol extraction-protein phosphatase methodology was 1.12 mg MCYST-LR equivalents/g dried bloom material. The analysis of this bloom extract by the LC/MS technique demonstrated the presence of three microcystin variants: microcystin-LR (MCYST-LR), microcystin-YR (MCYST-YR), and microcystin-RR (MCYST-RR). Microcystins were also detected in fresh carcasses of terrapin liver, viscera and muscle tissues using the GC/MS after Lemieux oxidation method and the PP2A inhibition assay. The high level of microcystins detected using the Lemieux oxidation-GC/MS method in the liver tissue (1192.8 microg MCYST-LR equivalent/g dw) and in the viscera tissue (37.19 microg MCYST-LR equivalent/g dw) of the species M. leprosa and E. orbicularis, respectively, and the liver crumbling observed after the necropsy examination of the fresh carcass of M. leprosa support the possibility that cyanobacterial microcystins contribute to the turtle mortalities.

Methods for determining microcystins (peptide hepatotoxins) and microcystin-producing cyanobacteria

Episodes of cyanobacterial toxic blooms and fatalities to animals and humans due to cyanobacterial toxins (CBT) are known worldwide. The hepatotoxins and neurotoxins (cyanotoxins) produced by bloom-forming cyanobacteria have been the cause of human and animal health hazards and even death. Prevailing concentration of cell bound endotoxin, exotoxin and the toxin variants depend on developmental stages of the bloom and the cyanobacterial (CB) species involved. Toxic and non-toxic strains do not show any predictable morphological difference. The current instrumental, immunological and molecular methods applied for determining microcystins (peptide hepatotoxins) and microcystin-producing cyanobacteria are reviewed.

Microcystin analysis in human sera and liver from human fatalities in Caruaru, Brazil 1996

In 1996, an extensive exposure of Brazilian hemodialysis patients at a dialysis center, using a municipal water supply water contaminated with cyanotoxins, provided the first evidence for acute lethal human poisoning from the cyclic peptide hepatotoxins called microcystins. During this outbreak, 100 of 131 patients developed acute liver failure and 52 of these victims were confirmed to have been exposed to lethal levels of microcystins. Detection and quantitation of microcystins in these biological samples posed some analytical challenges since there were no well-established and routine analytic methods to measure total microcystins in tissue or sera samples. At the time of the 1996 exposure we used analytic methods that combined the use of enzyme linked immunosorbant assay (ELISA), analytical high performance liquid chromatography (HPLC), electrospray ionization ion-trap mass spectroscopy (ES-ITMS) and matrix assisted laser desorption ionization-time of flight spectroscopy (MALDI-TOF). In the intervening years these methods have been improved and others developed that allow a more quantitative and critical analysis of microcystin contaminated tissue and sera. For these reasons, and to see how storage with time might effect the detection and stability of microcystins in these matrices, we reanalyzed selected liver tissues and sera from the Caruaru victims in Brazil. We developed and validated a procedure to measure total microcystins in Caruaru human sera and liver tissue using a combination of ELISA, liquid chromatography and liquid chromatography-mass spectrometry (LC/MS), GC/MS and MS/MS techniques. GC/MS and LC/MS were followed by MS/MS to obtain a fingerprint fragment spectra for the microcystins. The validity of the extraction procedure for free microcystins was confirmed by recovery experiments with blood sera spiked with microcystin-LR. We removed proteins with the Microcon Centrifugal Filter prior to LC/MS and ELISA analysis. A solid phase extraction (SPE) procedure was used for analysis of protein bound microcystins by conversion of ADDA to erythro-2-methyl-3-methoxy-4-phenylbutyric acid (MMPB) combined with GC/MS. We found that the GC/MS method yielded a higher concentration of microcystin than that obtained by ELISA and LC/MS. We hypothesize that this difference is due to better GC/MS detection of the covalently bound form of microcystins in human liver tissue. We also concluded that microcystins are very stable when stored under these conditions for periods of almost 10 years.

Optimization of an effective extraction procedure for the analysis of microcystins in soils and lake sediments

Microcystin analysis in sediments and soils is considered very difficult due to low recovery for extraction. This is the primary limiting factor for understanding the fate of toxins in the interface between water and sediment in both the aquatic ecosystem as well as in soils. In the present study, a wide range of extraction solvents were evaluated over a wide range of pH, extraction approaches and equilibration time to optimize an effective extraction procedure for the analysis of microcystins in soils and lake sediments. The number of extractions required and acids in extraction solutions were also studied. In this procedure, EDTA-sodium pyrophosphate solution was selected as an extraction solvent based on the adsorption mechanism study. The optimized procedure proved to be highly efficient and achieved over 90% recovery. Finally, the developed procedure was applied to field soil and sediment sample collected from Chinese lakes during bloom seasons and microcystins were determined in six of ten samples.

Kinetics of the oxidation of MCRR by potassium permanganate

The occurrence of the microcystins in the water bodies, especially in drinking water resources, has received considerable attentions. In situ chemical oxidation is a promising cost-effective treatment method to remove MC from water body. This research investigated the reaction kinetics of the oxidation of MCRR by permanganate. Experimental results indicate that the reaction is second order overall and first order with respect to both permanganate and MCRR, and has an activation energy of 18.9 kJ/mol. The second-order rate constant ranges from 0.154 to 0.225 l/mg/min at temperature from 15 to 30 degrees C. The MCRR degradation rates can be accelerated through increasing reaction temperature and oxidant concentration. The reaction under acid conditions was slightly faster than under alkaline conditions. The half-life of the reaction was less than 1min, and more than 99.5% of MCRR was degraded within 10min.

Chronic toxicity and responses of several important enzymes in Daphnia magna on exposure to sublethal microcystin-LR

In the current study, the toxicological mechanisms of microcystin-LR and its disadvantageous effects on Daphnia magna were examined. Survival rate, number of newborn, activity of several important enzymes [glutathione S-transferase (GST), lactate dehydrogenase (LDH), phosphatases, and glutathione], accumulated microcystins, and ultrastructural changes in different organs of Daphnia were monitored over the course of 21-day chronic tests. The results indicated that low concentrations of dissolved microcystin had no harmful effect on Daphnia. On the contrary, stimulatory effects were detected. In the presence of toxin at high dosage and for long-term exposure, GST and glutathione levels decreased significantly. The decreased enzyme activity in the antioxidant system probably was caused by detoxification reactions with toxins. And these processes of detoxification at the beginning of chronic tests may enable phosphatases in Daphnia magna to withstand inhibition by the toxins. At the same time, we also found that the LDH activity in test animals increased with exposure to microcystin-LR, indicating that adverse effects occurred in Daphnia. With microcystin given at a higher dosage or for a longer exposure, the effect on Daphnia magna was fatal. In the meantime, microcystin began to accumulate in Daphnia magna, and phosphatase activity started to be inhibited. From the ultrastructure results of cells in D. magna, we obtained new information: the alimentary canal may be the target organ affected by exposure of microcystins to D. magna. The results of the current study also suggested that the oxidative damage and PPI (protein phosphatase inhibition) mechanisms of vertebrates also are adapted to Daphnia.

Detection of the cyanobacterial hepatotoxins microcystins

Concern regarding the presence of microcystins in drinking water and their possible contamination in food (e.g., salad vegetables, fish, shellfish) has resulted in the need for reliable methods for the detection and accurate quantification of this class of toxins. Currently, routine analysis of microcystins is most commonly carried out using high-performance liquid chromatography with photodiode array detection (HPLC-PDA), although more sensitive biological assays such as antibody-based ELISAs and protein phosphatase inhibition assays have also proven useful. However, many of these methods have been hindered by the availability of a wide range of purified microcystins. Although over 60 variants have now been reported, only a very small number are commercially available and calibrated standards are not yet obtainable. This has led to the common practice of reporting microcystin-LR equivalence regardless of which variant is present. The increased availability of HPLC with online mass spectral analysis (HPLC-MS) may facilitate more accurate detection of toxin variants but as several microcystins share the same molecular mass, definitive identification can be difficult. A further difficulty in analyzing microcystins is the requirement for sample processing before analysis. Solid phase extraction (SPE) is typically used to enrich environmental concentrations of microcystins, or to eliminate contaminants from complex samples such as animal and plant tissues. Recently, new technologies employing recombinant antibodies and molecularly imprinted polymers have been exploited to develop assays and biosensors for microcystins. These novel detection systems are highly sensitive, often do not require sample processing, and offer a simpler, less expensive alternative to analytical techniques. They have also been successfully employed in solid phase extraction formats for the concentration and clean up of environmental samples before HPLC analysis.

Selective control of toxic Microcystis water blooms using lysine and malonic acid: an enclosure experiment

Three enclosures (10 x 10 x 1.5-1.3 m in depth) were set beside Dianch Lake, Kunming, People's Republic of China, for the period from July 28 to August 26, 2002. The enclosures were filled with cyanobacterial (Microcystis aeruginosa) water bloom-containing lake water. Lake sediment that contained macrophytes and water chestnut seeds was spread over the entire bottom of each enclosure. Initially, 10 g/m(2) of lysine was sprayed in Enclosure B, and 10 g/m(2) each of lysine and malonic acid were sprayed together in Enclosure C. Enclosure A remained untreated and was used as a control. The concentrations of lysine, malonic acid, chlorophyll a, and microcystin as well as the cell numbers of phytoplankton such as cyanobacteria, diatom, and euglena were monitored. On day 1 of the treatment, formation of cyanobacterial blooms almost ceased in Enclosures B and C, although Microcystis cells in the control still formed blooms. On day 7 Microcystis cells in Enclosure B that had been treated with lysine started growing again, whereas growth was not observed in Microcystis cells in Enclosure C, which had been treated with lysine and malonic acid. On day 28 the surface of Enclosure B was covered with water chestnut (Trapa spp.) and the Microcystis blooms again increased. In contrast, growth of macrophytes (Myriophllum spicatum and Potamogeton crispus) was observed in Enclosure C; however, no cyanobacterial blooms were observed. Lysine and malonic acid had completely decomposed. The microcystin concentration on day 28 decreased to 25% of the initial value, and the pH shifted from the initial value of 9.2 to 7.8. We concluded that combined treatment with lysine and malonic acid selectively controlled toxic Microcystis water blooms and induced the growth of macrophytes.